This invention is related to a heat transfer method and apparatus, and more specifically to a method and apparatus for efficiently transferring heat energy from a primary heated fluid to heat a secondary medium, such as a bridge deck, isothermally.
In a variety of industrial and commerical situations, it is desirable to utilize the energy from a primary source of heated fluid to heat a different medium. In most such applications, a conventional heat exchanger can be utilized wherein the primary heated fluid can be brought into close proximity with the medium to be heated and allow the heat to transfer by conduction from the primary heated fluid to the medium to be heated. However, there are situations in which it is not desirable to conduct the primary heated fluid into close proximity with the medium to be heated. An example of such a use is where it is desired to utilize geothermally heated water to heat a road surface, such as a road surface on a bridge deck, to prevent the formation of ice and snow thereon. The U.S. Pat. No. 3,580,330, invented by P. Maugis, discloses the use of geothermally heated water for such heating purposes as urban heating, and U.S. Pat. No. 3,521,699, issued to A. T. Van Huisen, discloses the use of geothermally heated water to heat agricultural lands as well as to heat road surfaces. However, there are some significant problems associated with such systems that flow the geothermally heated water through pipes embedded directly in road surfaces on highways, bridges, runaways and the like, since a variety of failure modes can and often do lead to freezing of the water in the embedded pipes causing fracture of the piping as well as fracturing the road or bridge surface in which the pipes are embedded. Also, during such failure, large quantities of water could be leaked onto the road or runway surface and freeze in a cold atmosphere causing severely hazardous slippery conditions on the road surface.
It is also known in the prior art to utilize latent heat in the ground to heat road surfaces by the use of devices, commonly referred to as heat pipes to transfer the heat from the ground to the road surface. Such heat pipe devices are disclosed in the U.S. patents issued to J. Tippman, U.S. Pat. No. 3,195,619, to E. Faccini, U.S. Pat. No. 4,162,394, and W. Bienert et al, U.S. Pat. No. 4,050,509. Such heat pipe devices generally include an elongated vertical section driven a substantial distance into the ground and a horizontal section extending into the road surface. The Tippman device also discloses several horizontal or condenser portions branching off from the vertical section of the pipe. The interior of such heat pipes usually have a volatile liquid, such as ammonia, placed therein, which vaporizes due to the heat in the ground. The vapor migrates upwardly through the pipe to the road surface where it comes in contact with cooler portions of the pipe. Upon entering the cooler zone, the vapor condenses and gives up its heat of vaporization in the roadway surface. While such conventional heat pipe arrangements have been beneficial in heating road surfaces, there are still a number of problems that have not heretofore been solved by them. For example, in mountainous or rocky terrain it is impractical or at least quite costly to drive or embed the vertical portions of the heat pipes a sufficient distance into the ground to tap a sufficient heat source for heating the road. Extended periods of cold atmospheric conditions tend to deplete the heat source in the immediate vicinity of the ground adjacent the heat pipes so that the available heat is insufficient to keep the road surface above freezing. The down-pumping heat pipes in the Bienert et al patent, U.S. Pat. No. 4,050,509, provide one at least partial solution for this problem. The distance between the ground and bridge decks cause additional costs, heat loss, and other problems that detract from the economy and effectiveness of conventional heat pipe apparatus for use in heating bridge decks. Also, the heat transferred from the ground to the road surface by such heat pipe devices tends to be localized and temperatures vary substantially over a range of road surface many times resulting in localized patches of ice or snow forming on some portions of the road surface. This problem is particularly aggrevated on bridge surfaces where some portions of the bridge deck might be shaded from the sun while other adjacent portions are heated by the sun's rays.
There exists a need therefore for an apparatus capable of transferring heat from geothermally heated fluid to a road surface on a bridge deck or the like without allowing the geothermal water or steam to come in contact with the road surface, as well as to distribute the heat over a section of the road surface in an isothermal manner to compensate for areas that might receive varying or different amounts of heat or cold from the sun as it changes position in the sky, or from wind, snow and the like.